Piezoelectric resonator and electronic component containing same

ABSTRACT

A piezoelectric resonator has a base member including laminated piezoelectric layers and internal electrodes. The base member is polarized in different directions at both sides of each internal electrode. The internal electrodes are alternately covered by insulating film on opposing side surfaces of the base member. External electrodes are formed on the opposing side surfaces of the base member and the internal electrodes are connected thereto, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to novel piezoelectric resonators andelectronic components containing such novel piezoelectric resonators,and more particularly, to a novel piezoelectric resonator whichmaximizes the effective use of the mechanical resonance of apiezoelectric member, and electronic components containing such a novelpiezoelectric resonator, such as an oscillator, a discriminator, and afilter.

2. Description of the Related Art

FIG. 40 is a perspective view of a conventional piezoelectric resonator.A piezoelectric resonator 1 includes a single piezoelectric substrate 2having, for example, a rectangular plate shape as viewed from above. Thesingle piezoelectric substrate 2 is polarized in the thicknessdirection. On two opposite major surfaces of the piezoelectric substrate2, electrodes 3 are provided. When a signal is input between theelectrodes 3, an electrical field is applied to the single piezoelectricsubstrate 2 in the thickness direction and the single piezoelectricsubstrate 2 vibrates in the longitudinal direction.

In FIG. 41, there is shown a piezoelectric resonator 1 in whichelectrodes 3 are provided on both surfaces of a single piezoelectricsubstrate 2 having a square plate shape as viewed from above. The singlepiezoelectric substrate 2 of the piezoelectric resonator 1 is polarizedin the thickness direction. When a signal is input between theelectrodes 3 in the piezoelectric resonator 1, an electrical field isapplied to the single piezoelectric substrate 2 in the thicknessdirection and the single piezoelectric substrate 2 vibrates insquare-type vibration mode (in the plane direction).

Because the piezoelectric substrate of the piezoelectric resonator shownin FIG. 40 has a rectangular plate shape, the substrate cannot be madethinner because of restrictions in strength. Therefore, the distancebetween the electrodes cannot be reduced and a capacitance betweenterminals cannot be increased. This makes it extremely difficult toachieve impedance matching with an external circuit. To form a ladderfilter by alternately connecting a plurality of piezoelectric resonatorsin series and in parallel, the capacitance ratio of the series resonatorto the parallel resonator needs to be made large in order to increaseattenuation. Because a piezoelectric resonator has the shape andstructural limitations described above, however, large attenuationcannot be obtained.

Such a piezoelectric resonator 1 uses the first-order resonance in thelongitudinal mode. Because of its structure, the piezoelectric resonator1 generates large spurious resonances in odd-number-order harmonicmodes, such as the third-order and fifth-order modes, and in width mode.To suppress these spurious resonances, some solutions have beenconsidered, such as polishing, increasing mass, and changing the shapeof the electrode. These solutions increase manufacturing cost.

In the piezoelectric resonator shown in FIG. 41, large spuriousresonances such as those in the thickness mode and in the triple-wavemode in the plane direction are generated. Since the piezoelectricresonator must have a large size as compared with a piezoelectricresonator using the longitudinal vibration in order to obtain the sameresonant frequency, it is difficult to reduce the size of thepiezoelectric resonator. When a ladder filter is formed by a pluralityof piezoelectric resonators, in order to increase the capacitance ratiobetween the series resonator and the parallel resonator, the resonatorsconnected in series must have an increased thickness and electrodes areformed only on part of a piezoelectric substrate to make the capacitancesmall. In this case, since the electrodes are only partially formed, thedifference ΔF between the resonant frequency and the antiresonantfrequency as well as the capacitance is reduced. The resonatorsconnected in parallel are accordingly required to have small ΔF. As aresult, the piezoelectricity of the piezoelectric substrate is noteffectively used, and the transmission band width of the filter cannotbe increased.

These piezoelectric resonators shown in FIGS. 40 and 41 are ofunstiffened type resonators, in which the vibration direction differsfrom the direction of polarization and the electrical field. Theelectromechanical coupling coefficient of such an unstiffenedpiezoelectric resonator is lower than that of a stiffened piezoelectricresonator, in which the vibration direction, the direction ofpolarization, and the direction in which an electrical field is appliedare the same.

An unstiffened piezoelectric resonator has a relatively small frequencydifference ΔF between the resonant frequency and the antiresonantfrequency. This leads to a drawback in which a frequency-band width inuse is narrow when an unstiffened frequency resonator is used as anoscillator or a filter. Therefore, the degree of flexibility and freedomin resonator characteristics design is low in such unstiffenedpiezoelectric resonators and electronic components containing suchpiezoelectric resonators.

In the prior art, such as U.S. Pat. No. 5,250,868, a piezoelectriceffect device includes a sintered stack of piezoelectric elements whichstack is completely enclosed in a flexible metal housing to be used asan actuator. The stack includes non-active portions I₁ and I_(n) locatedat the ends of the stack for protecting the active portions I₂ through1_(n-1). In order to function as an actuator, the stack 3 ofpiezoelectric elements must be supported at one end and must be free tovibrate in a longitudinal mode at the other end. Thus, the stack 3 couldnot be supported at a point other than the one end and therefore, thestack 3 could not be supported at a central or middle portion of thestack 3 without destroying the operability of the stack 3 as anactuator. In addition, the stack 3 of piezoelectric elements mustachieve maximum displacement required for actuators and therefore, thestack 3 must have a node point located only at the supported end of thestack 3. The stack 3 cannot have a node point located at a central ormiddle portion of the stack, otherwise the stack 3 could not function asan actuator. By arranging the stack 3 to have a node point at one endand to be supported at the same end, the stack 3 can achieve the maximumdesired displacement necessary in an actuator.

In addition, U.S. Pat. No. 4,633,120 teaches an electrostrictiontransducer including a plurality of electrostriction layers, notpiezoelectric layers, stacked on each other and including protection ordummy layers on each end of the stack of electrostriction layers forprotecting the stack of electrostrictive layers. The electrostrictionlayers are very different from piezoelectric elements and cannotfunction in the same manner as piezoelectric elements, as is well known.

The prior art stacked devices are only adapted to function as anactuator or electrostrictive transducer, and could not function as aresonator. Therefore, a location of a resonant point and ananti-resonant point and an amount of capacitance is of no concern inthese types of devices. Accordingly, the prior art stacked devices haveelectrodes provided at both ends of the stack of piezoelectric orelectrostriction members. These electrodes cannot be located along alongitudinal side edge of the stack in order for the stacked devices tofunction as an actuator or transducer. Furthermore, these prior artdevices cannot have a node located at a central or middle portion of astack of piezoelectric elements or be supported at a node located at acentral or middle portion of the stack.

In addition, the only purpose for providing the protection or dummylayer is to protect the piezoelectric or electrostriction layerssurrounded by the protection or dummy layers. The stacked piezoelectricor electrostrictive layers of the prior art are not arranged or adaptedto function as a resonator which can be used in an oscillator, adiscriminator, or a filter.

SUMMARY OF THE INVENTION

The preferred embodiments of the present invention provide apiezoelectric resonator having a small spurious resonance, a largedifference ΔF between the resonant frequency and the antiresonantfrequency, an easily adjustable location of a resonant point and anantiresonant point, an easily adjustable capacitance and ΔF, and a largedegree of freedom and flexibility in resonator characteristics design,and also provide an electronic component containing such a novelpiezoelectric resonator.

The preferred embodiments of the present invention also provide apiezoelectric resonator including a piezoelectric base member comprisesan integral unit including a plurality of interconnected piezoelectriclayers or members and a plurality of electrodes disposed between saidpiezoelectric layers.

The preferred embodiments of the present invention also provide apiezoelectric resonator including a piezoelectric base member comprisinga stack of a plurality of interconnected piezoelectric layers each ofwhich is adapted to vibrate individually in a thickness vibration modesuch that the stack of interconnected piezoelectric layers vibrate as awhole in a longitudinal vibration mode.

The preferred embodiments of the present invention further provide apiezoelectric resonator including a piezoelectric base member comprisesan integral unit including a plurality of interconnected piezoelectriclayers or members and a plurality of electrodes disposed between saidpiezoelectric layers, wherein each of the piezoelectric layers locatedbetween adjacent ones of the electrodes is polarized in a direction thatis opposite to a direction of polarization of at least one adjacentpiezoelectric layer. That is, the base member is preferably polarized inopposite directions at both sides of at least one of the electrodes.

According to one preferred embodiment of the present invention, apiezoelectric resonator comprises a base member; a plurality of internalelectrodes disposed in the base member so as to be substantiallyperpendicular to a longitudinal direction of the base member; and onepair of external electrodes provided on a common side surface ordifferent side surfaces of the base member to connect the plurality ofinternal electrodes; wherein the base member includes an integral unitincluding a plurality of piezoelectric layers and the plurality ofinternal electrodes which are alternately laminated, and an AC electricfield is applied to each of the piezoelectric layers via the pluralityof internal electrodes such that the base member generates longitudinalbasic vibration.

The piezoelectric resonator according to the preferred embodiments ofthe present invention may be configured such that the plurality ofpiezoelectric layers are polarized in the longitudinal direction of thebase member in opposite directions at each side of each of the pluralityof internal electrodes, and adjacent electrodes of the plurality ofinternal electrodes are alternately connected to one of the externalelectrodes, respectively.

The piezoelectric resonator may be configured such that it furtherincludes at least one pair of connection sections in which alternateexposed sections of the plurality of internal electrodes are covered byinsulating films, each of the plurality of internal electrodes is formedto cover an entire surface of a cross section of the base member, andthe one pair of external electrodes is disposed on the one pair ofconnection sections such that adjacent internal electrodes among theplurality of internal electrodes are alternately connected to one of thepair of external electrodes, respectively.

The piezoelectric resonator may also be configured such that a part ofeach of the plurality of internal electrodes is arranged so as not to beexposed at side surfaces of the base member, and the exposed sections ofthe plurality of internal electrodes are connected to the one pair ofexternal electrodes such that adjacent internal electrodes among theplurality of internal electrodes are alternately connected to one of thepair of external electrodes, respectively.

The piezoelectric resonator may also be configured such that the basemember is provided with at least either an inactive section which is notpolarized or an inactive section to which no electric field has beenapplied.

In a preferred embodiment, an active section constitutes a centralportion of the piezoelectric base member and there are two inactivesections each provided at one of the ends of the active section suchthat the active section is surrounded by inactive sections at oppositeends thereof. The piezoelectric base member is preferably arranged suchthat a node is defined at a center or midpoint of the active sectionthereby allowing the piezoelectric resonator to be supported at the nodewithout affecting the resonator characteristics.

The inactive section may be formed in many ways. First, the inactivesection may be formed without an electrode material disposed thereon. Asa result, the inactive section without an electrode cannot be polarizedor receive an electric field. Alternatively, the inactive section may beprovided with an electrode material but the inactive section is notpolarized so it does not generate vibration, and is therefore inactive.

Although one or more inactive sections may be disposed at any locationwithin the base member, it is preferred in the piezoelectric resonatorof the preferred embodiments of the present invention that the inactivesection be provided at the two opposite ends of the active section, andthe active section preferably occupies about 50% of a length of the basemember.

The piezoelectric resonator may further include a support member, and amounting member disposed between the support member and preferably anapproximate center section of the base member.

Another preferred embodiment of the present invention provides anelectronic component containing the above-described piezoelectricresonator, wherein the support member comprises an insulating substrateon which a pattern electrode is provided; the base member is mounted onthe insulating substrate via the mounting member; and a cap ispreferably disposed on the insulating substrate so as to cover the basemember.

Another preferred embodiment of the present invention provides anelectronic component containing the above-described piezoelectricresonator, wherein the support member comprises an insulating substrateon which a pattern electrode is provided; a plurality of base membersare mounted on the insulating substrate via the mounting member so as todefine a ladder filter; and a cap is preferably disposed on theinsulating substrate so as to cover the base member.

As a result of the structure and novel arrangement of the piezoelectricresonator according to the preferred embodiments of the presentinvention having a base member comprising piezoelectric layers andelectrodes which are alternately laminated, the capacitance of thepiezoelectric resonator can be easily changed by adjusting theintervals, the sizes, or the number of electrodes used for applying anelectric field to the base member. When such a piezoelectric resonatoris constructed such that the vibration direction, the direction ofpolarization, and the direction in which an electrical field is appliedare the same in the piezoelectric layers, the resonator is a stiffenedtype resonator. Therefore, as compared with an unstiffened piezoelectricresonator, in which the vibration direction differs from the directionof polarization and electrical field, the stiffened piezoelectricresonator has a larger electromechanical coupling coefficient and alarger frequency difference ΔF between the resonant frequency and theantiresonant frequency. In addition, vibrations in modes such as thewidth and thickness modes, which are different from the longitudinalbasic vibration, are unlikely to occur in a stiffened piezoelectricresonator. Furthermore, the frequency difference ΔF and the resonantfrequency can be easily adjusted by reducing or increasing a size ormass of an inactive section.

When electronic components such as an oscillator, a discriminator, and afilter are constructed to include the piezoelectric resonator accordingto the preferred embodiments of the present invention, the piezoelectricresonator is preferably mounted on an insulating substrate on whichpattern electrodes are provided and the resonator is preferably coveredby a cap to form chip-type, surface-mountable electronic components.

According to the preferred embodiments of the present invention, sincethe capacitance of the piezoelectric resonator can be easily adjusted,it is easy to achieve impedance matching with an external circuit whenthe piezoelectric resonator is mounted on a circuit board. When thepiezoelectric resonator is a stiffened type resonator, the frequencydifference ΔF between the resonant frequency and the antiresonantfrequency is large as compared with a conventional piezoelectricresonator, and thus a wide-frequency-band resonator is obtained. Inaddition, vibrations in modes other than the basic-vibration mode areunlikely to occur in this piezoelectric resonator, and superiorresonator characteristics are achieved. Since the frequency differenceΔF is easily adjusted by adjusting the inactive section, thefrequency-band width of the piezoelectric resonator can easily bechanged.

Since a chip-type electronic component can be constructed using thepiezoelectric resonator of the preferred embodiments of the presentinvention, it is easy to mount the component on a circuit board. It isalso easy to achieve impedance matching between such an electroniccomponent and an external circuit by adjusting the capacitance of thepiezoelectric resonator. In addition, in a ladder filter formed byalternately connecting a plurality of piezoelectric resonators in seriesand in parallel, attenuation in the filter can be adjusted by changingthe ratio of the capacitance of the piezoelectric resonator connected inseries to that of the piezoelectric resonator connected in parallel.

These and other elements, features, and advantages of the preferredembodiments of the present invention will be apparent from the followingdetailed description of the preferred embodiments of the presentinvention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a piezoelectric resonator according to apreferred embodiment of the present invention.

FIG. 2 is a view showing the structure of the piezoelectric resonatorshown in FIG. 1.

FIG. 3 is a perspective view indicating how ceramic green sheets arelaminated in order to produce the piezoelectric resonator shown in FIG.1.

FIG. 4 is a view showing a laminated block formed by the ceramic greensheets shown in FIG. 3.

FIG. 5 is a view showing portions where the laminated block shown inFIG. 4 is cut.

FIG. 6 is a view showing a plate-shaped block made by cutting thelaminated block shown in FIG. 5.

FIG. 7 is a view showing the condition in which a resin insulatingmaterial is applied to the plate-shaped block shown in FIG. 6 andexternal electrodes are formed.

FIG. 8 is a perspective view of an unstiffened piezoelectric resonatorwhich vibrates in the longitudinal direction, which is shown forcomparison.

FIG. 9 is a perspective view of a stiffened piezoelectric resonatorwhich vibrates in the longitudinal direction.

FIG. 10 is a perspective view of an unstiffened piezoelectric resonatorwhich vibrates in the plane direction (square-type vibration), which isshown for comparison.

FIG. 11 is a view showing another piezoelectric resonator according tothe preferred embodiments of the present invention.

FIG. 12 is a view showing still another piezoelectric resonatoraccording to the preferred embodiments of the present invention.

FIG. 13 is a chart showing the relationship between the frequency andthe impedance of the piezoelectric resonator according to the preferredembodiments of the present invention.

FIG. 14 is a chart showing the relationship between the frequency andthe impedance of a conventional piezoelectric resonator.

FIG. 15 is a view of a piezoelectric resonator in which the distributionof an active section and inactive sections is changed in a base member.

FIG. 16 is a chart indicating the relationship between the distributionof an active section and capacitance, and ΔF/Fa.

FIG. 17 is a chart showing the relationship between an active-sectionratio and ΔF.

FIG. 18 is a view showing a modified piezoelectric resonator accordingto the preferred embodiments of the present invention.

FIG. 19 is a view showing another modified piezoelectric resonatoraccording to the preferred embodiments of the present invention.

FIG. 20 is a view showing still another piezoelectric resonatoraccording to the preferred embodiments of the present invention.

FIG. 21 is a view indicating the gap between the end of an internalelectrode and a side surface of a base member in the piezoelectricresonator.

FIG. 22 is a chart indicating the relationships between the capacitanceand ΔF, and the gap between an internal electrode and a side surface ofthe base member.

FIG. 23 is a plan showing modified piezoelectric layers of thepiezoelectric resonator shown in FIG. 20.

FIG. 24 is a view showing a piezoelectric resonator having thepiezoelectric layers shown in FIG. 23.

FIG. 25 is a view showing a modified inactive section of a piezoelectricresonator.

FIG. 26 is a view showing another modified inactive section of apiezoelectric resonator.

FIG. 27 is a view showing an electrode formed at an end of a basemember.

FIG. 28 is a perspective view of an electronic component containing theabove-described piezoelectric resonator.

FIG. 29 is a perspective view of an insulating substrate provided in theelectronic component shown in FIG. 28.

FIG. 30 is an exploded perspective view of the electronic componentshown in FIG. 28.

FIG. 31 is a view indicating another method for mounting thepiezoelectric resonator o the insulating substrate.

FIG. 32 is a side view showing the method for mounting the piezoelectricresonator, shown in FIG. 31.

FIG. 33 is a view indicating still another method for mounting thepiezoelectric resonator on the insulating substrate.

FIG. 34 is a side view showing the method for mounting the piezoelectricresonator, shown in FIG. 33.

FIG. 35 is an exploded perspective view of a ladder filter using thepiezoelectric resonators according to the preferred embodiments of thepresent invention.

FIG. 36 is a perspective view of an insulating substrate and thepiezoelectric resonators in the ladder filter shown in FIG. 35.

FIG. 37 is an equivalent circuit diagram of the ladder filter shown inFIG. 35.

FIG. 38 is an exploded perspective view of a two-terminal electroniccomponent.

FIG. 39 is a chart indicating the relationship between Cf and ΔF/Fa, andother parameters.

FIG. 40 is a view of a conventional unstiffened piezoelectric resonator.

FIG. 41 is a view of another conventional unstiffened piezoelectricresonator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of a piezoelectric resonator according to apreferred embodiment of the present invention. FIG. 2 shows the internalstructure of the piezoelectric resonator. The piezoelectric resonator 10includes a base member 12 preferably having, for example, asubstantially rectangular-parallelpiped shape. The base member 12 ismade from, for example, a piezoelectric ceramic material. A plurality ofelectrodes 14 are provided in the base member 12 and preferably at bothend surfaces of the base member 12 in the longitudinal direction suchthat the surfaces of the electrodes 14 are substantially perpendicularto the longitudinal direction of the base member 12. The base member 12is preferably polarized in opposite directions at both sides of at leastone of the electrodes 14 as seen in FIG. 2.

On the opposing side surfaces of the base member 12, a plurality ofinsulating films 16 and 18 are provided, respectively. On a first sidesurface of the base member 12, the insulating film 16 covers the exposedsection of every other electrode 14. On a second side surface of thebase member 12, the insulating film 18 covers the exposed section ofevery other electrode 14 not covered by the insulating film 16 on thefirst side surface. The side surfaces of the base member 12 on which theinsulating films 16 and 18 are provided serve as connection sections toexternal electrodes, which will be described later.

In these connection sections, namely, the side surfaces of the basemember 12 on which the insulating films 16 and 18 are provided, externalelectrodes 20 and 22 are disposed. The electrode 20 connects toelectrodes 14 which are not covered by the insulating film 16, and theelectrode 22 connects to electrodes 14 which are not covered by theinsulating film 18. In other words, two adjacent electrodes 14 areconnected to the electrodes 20 and 22, respectively. The piezoelectricresonator 10 preferably uses the external electrodes 20 and 22 as inputand output electrodes. The base member 12 is piezoelectrically activebecause an electric field is applied between adjacent electrodes 14.

In a preferred embodiment of making the piezoelectric resonator 10,green sheets 30 made from piezoelectric ceramic are first prepared asshown in FIG. 3. On one surface of each green sheet 30, electricallyconductive paste including, for example, silver, palladium, and anorganic binder, is applied to form an electrically conductive pastelayer 32 over almost the entire area of each green sheet 30 excluding anend portion. A plurality of green sheets 30 is laminated such that theend portions where the electrically conductive paste layers 32 are notformed on the green sheets are placed alternately in oppositedirections. The laminated member with electrically conductive pasteapplied to opposite side faces is baked to form a laminated block 34shown in FIG. 4.

A plurality of electrodes 36, which have been made by baking theelectrically conductive layers 32, are formed in and at both ends of thelaminated block 34. External electrodes 38 and 40 disposed on oppositeside surfaces are connected to every other electrode 36, respectively,since the electrodes 36 are alternately exposed on opposite sidesurfaces of the laminated block 34. When a DC voltage is applied to theexternal electrodes 38 and 40, the laminated block 34 is polarized.Inside the laminated block 34, a high DC electric field is appliedbetween adjacent internal electrodes 36 alternately in oppositedirections. Therefore, the laminated block 34 is polarized in theopposite directions at both sides of the electrodes 36 as shown byarrows in FIG. 4.

The laminated block 34 preferably is surface-ground to the desiredthickness since the antiresonant frequency of the resonator isdetermined by the thickness of the laminated block 34. The laminatedblock 34 is cut by a dicing machine along dotted lines shown in FIG. 5such that the cutting planes are substantially perpendicular to theplurality of electrodes 36. Then, a plate-shaped block 42 shown in FIG.6 is obtained. A resin insulating material 44 is preferably applied toboth surfaces of the plate-shaped block 42 as shown in FIG. 7 such thatthe material 44 is applied to every other internal electrode 36 on onesurface and every other electrode 36 to which the material 44 is notapplied, on the other surface. External electrodes 48 are disposed onthe plate-shaped block 42. Then, the resultant block is cutsubstantially perpendicularly to the internal electrodes 36 to form thepiezoelectric resonator 10 shown in FIG. 1.

When a signal is applied to the external electrodes 20 and 22 in thepiezoelectric resonator 10, since voltages are applied in directionsopposite to the directions of polarization of the piezoelectric layersin the base member 12 which are polarized, the piezoelectric layerssimultaneously expand and contract as an integral unit in the samedirection. An AC electric field is preferably applied to eachpiezoelectric layer in the longitudinal direction of the base member 12via the electrodes 14 connected to the external electrodes 20 and 22,and a driving force for expansion and contraction is generated at eachpiezoelectric layer. Therefore, the piezoelectric resonator 10 isconstructed and arranged to vibrate in the longitudinal direction in abasic longitudinal vibration mode with the approximate center of thebase member 12 serving as a node.

As a result of the piezoelectric resonator 10 according to the preferredembodiments of the present invention having a structure in which aplurality of piezoelectric layers and electrodes are alternatelylaminated, the capacitance of the piezoelectric resonator 10 can beeasily changed by adjusting the number of the laminated layers, theelectrode size, or the distances between the electrodes. Therefore, itis easy to achieve impedance matching with an external circuit when thepiezoelectric resonator 10 is mounted on a circuit board.

In the piezoelectric resonator 10 shown in FIG. 1, the polarizationdirection of the base member 12, the applied electric field direction,and the direction of vibration in the base member 12 are all the same.In other words, the piezoelectric resonator 10 is a stiffened typeresonator. The stiffened piezoelectric resonator 10 has a largerelectromagnetic coupling coefficient than an unstiffened piezoelectricresonator, in which the direction of vibration differs from thedirection of polarization and electric field. Therefore, thepiezoelectric resonator 10 has a larger frequency difference ΔF betweenthe resonant frequency and the antiresonant frequency than theconventional piezoelectric resonator. As a result of this uniquestructure, the piezoelectric resonator 10 achieves wide-frequency-bandcharacteristics.

To measure differences between stiffened and unstiffened piezoelectricresonators, piezoelectric resonators shown in FIGS. 8, 9 and 10 weremade. The piezoelectric resonator shown

in FIG. 8 was made by forming electrodes on both surfaces in thethickness direction of a piezoelectric substrate measuring approximately4.0 mm by 1.0 mm by 0.38 mm. This piezoelectric resonator was polarizedin the thickness direction and vibrated in the longitudinal directionwhen a signal was applied to the electrodes. The piezoelectric resonatorshown in FIG. 9 had the same dimensions as the piezoelectric resonatorshown in FIG. 8. Electrodes were disposed on both surfaces in thelongitudinal direction of a piezoelectric substrate. The piezoelectricresonator was polarized in the longitudinal direction and vibrated inthe longitudinal direction when a signal was applied to the electrodes.The piezoelectric resonator shown in FIG. 10 was made by disposingelectrodes on both surfaces in the thickness direction of apiezoelectric substrate measuring approximately 4.7 mm by 4.7 mm by 0.38mm. This piezoelectric resonator was polarized in the thicknessdirection and vibrated in the plane direction when a signal was appliedto the electrodes. The piezoelectric resonators shown in FIGS. 8 and 10were unstiffened type resonators and the piezoelectric resonator shownin FIG. 9 was a stiffened type resonator.

The resonant frequency Fr and the electromechanical coupling coefficientK of each of these piezoelectric resonators were measured and theresults are shown in Tables 1, 2, and 3. Table 1 indicates the measuredresults of the piezoelectric resonator shown in FIG. 8. Table 2indicates the measured results of the piezoelectric resonator shown inFIG. 9. Table 3 indicates the measured results of the piezoelectricresonator shown in FIG. 10.

                  TABLE 1                                                         ______________________________________                                                 Basic     Longitudinal                                                        longitudinal                                                                            triple-wave                                                                             Width-mode                                                vibration vibration vibration                                        ______________________________________                                        Resonant frequency                                                                       0.460       1.32      1.95                                         (MHZ)                                                                         Electromechanical                                                                        18.9        3.9       25.2                                         coupling                                                                      coefficient (%)                                                               ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                 Basic     Longitudinal                                                        longitudinal                                                                            triple-wave                                                                             Width-mode                                                vibration vibration vibration                                        ______________________________________                                        Resonant freguency                                                                       0.455       1.44      1.96                                         (MHZ)                                                                         Electromechanical                                                                        42.9        12.2      4.0                                          coupling                                                                      coefficient (%)                                                               ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                 Basic     Square-type                                                                             Thickness-                                                longitudinal                                                                            triple-wave                                                                             mode                                                      vibration vibration vibration                                        ______________________________________                                        Resonant frequency                                                                       0.458       1.25      5.65                                         (MHZ)                                                                         Electromechanical                                                                        35.0        11.5      23.3                                         coupling                                                                      coefficient (%)                                                               ______________________________________                                    

It is understood from the measurement data that a stiffenedpiezoelectric resonator has a larger electromagnetic couplingcoefficient K than an unstiffened piezoelectric resonator, and thereforehas a larger frequency difference ΔF between the resonant frequency andthe antiresonant frequency. The largest spurious vibration in astiffened piezoelectric resonator is a longitudinal triple-wave type andthe electromagnetic coupling coefficient K is 12.2% during vibration.During width-mode vibration, which is different from basic vibration,the electromagnetic coupling coefficient K is 4.0%. In contrast, theelectromagnetic coupling coefficient K during width-mode vibration is25.2% in an unstiffened longitudinal-vibration piezoelectric resonator.In an unstiffened square-type vibration piezoelectric resonator, theelectromagnetic coupling coefficient K is as large as 23.3% duringthickness-mode vibration. Therefore, it is understood that a stiffenedpiezoelectric resonator has smaller spurious vibrations than anunstiffened piezoelectric resonator.

In order to connect the electrodes 14 provided in the base member 12 tothe external electrodes 20 and 22, internal electrodes 14 mayalternately extend to opposite side surfaces of the base member 12 asshown in FIG. 11. On the opposite side surfaces of the base member 12,external electrodes 20 and 22 are provided. In the piezoelectricresonator 10, since the electrodes 14 are exposed alternately, thealternate electrodes 14 are connected to the external electrodes 20 and22, respectively, by disposing the external electrodes 20 and 22 on theside surfaces of the base member 12. Therefore, there is no need toprovide insulating film on the side surfaces of the base member 12. Anelectrode 14 is preferably not formed so as to cover the entire area ofa cross section of the base member 12 in this piezoelectric resonator10. Therefore, an opposing area of adjacent electrodes 14 is smallerthan that of adjacent electrodes 14 which are preferably formed to coverthe entire cross section of the base member 12. By changing the opposingarea of the electrodes 14, the capacitance and ΔF of the piezoelectricresonator 10 can be easily adjusted.

As shown in FIG. 12, an active section which is piezoelectrically activeand an inactive section which is piezoelectrically inactive can beprovided in the base member 12 of the piezoelectric resonator 10. Inthis case, for example, electrodes 14 are not provided at the oppositeend surfaces of the base member 12, and some electrodes 14 disposed nearopposite end surfaces of the base member 12 are preferably successivelycovered by the insulating films 16 and 18. In this preferred embodiment,three consecutive electrodes 14 located at each end of the base member12 are preferably covered by the insulating film 16, and two consecutiveelectrodes 14 located at each end of the base member 12 are covered bythe insulating film 18. External electrodes 20 and 22 are provided onthe side surfaces of the base member 12 on which the insulating films 16and 18 are disposed. The internal electrodes 14 are thereby connected tothe external electrodes 20 and 22. Some of the electrodes 14 disposed atthe opposite ends of the base member 12 are, however, not connected tothe external electrodes 20 and 22.

At the approximate center of the base member 12, the base member 12 ispreferably piezoelectrically active because an electric field is appliedbetween adjacent electrodes 14. The base member 12 is preferablypiezoelectrically inactive at opposite ends thereof because an electricfield is not applied between adjacent electrodes 14 since the electrodes14 are insulated. Therefore, an active section 24 for receiving inputsignals is defined at the approximate center portion of the base member12 as shown by hatching in FIG. 12. Inactive sections 26 which do notrespond to input signals are also preferably defined at the oppositeends of the base member 12.

In the piezoelectric resonator 10, the inactive section 26 is preferablyprovided at both ends of the base member 12. The inactive section 26 isadapted to be easily changed to adjust the resonant frequency and thedifference ΔF between the resonant frequency and the antiresonantfrequency. For example, by grinding the end surfaces in the longitudinaldirection of the base member 12 or by adding mass to the inactivesection, the resonant frequency and/or the antiresonant frequency of thepiezoelectric resonator 10 can easily be adjusted.

In the piezoelectric resonator 10, as described before, the capacitanceof the resonator can easily be adjusted by, for example, changing thenumber of piezoelectric layers in the base member 12. In the base member12, the piezoelectric layers and electrodes 14 are preferablyalternately stacked and electrically connected in parallel. When thenumber of layers is changed with the total length of the base member 12remaining constant, the following relationship is satisfied since thethickness of one layer is inversely proportional to the number oflayers:

Capacitance of resonator ∝ (the number of layers in activesection/thickness of a layer) ∝ (the number of layers in activesection)²

wherein the symbol ∝ is defined as "is proportional to." Thus, thecapacitance of the resonator is proportional to the square of the numberof layers in the active section of the base member 12. Therefore, thenumber of layers in the active section of the base member 12 is easilychanged to adjust the capacitance of the piezoelectric resonator 10.This structural arrangement results in the piezoelectric resonator 10having a high degree of freedom and flexibility in capacitance design.Therefore, it is easy to achieve impedance matching with an externalcircuit when the piezoelectric resonator 10 is mounted on a circuitboard.

In another example, electrically conductive paste including, forexample, silver, palladium, and an organic binder, was applied to onesurface of each green sheet 30 made from piezoelectric ceramic. Aplurality of such green sheets were stacked alternately and bakedintegrally at about 1200° C. to form a laminated block 34 measuringapproximately 20 mm by 30 mm by 3.9 mm. External electrodes 38 and 40were formed by sputtering. A high DC electric field was applied betweenadjacent internal electrodes 36 to polarize the laminated block suchthat the directions of polarization in adjacent piezoelectric layerswere alternately opposed. The thickness of the laminated block 34 waschanged. The laminated block 34 was cut to form a plate-shaped block 42measuring approximately 1.5 mm by 30 mm by 3.8 mm. Every other electrode36 exposed at the side surfaces of the plate-shaped block 42 werecovered by a resin insulating material 44 and a silver electrode wasdisposed thereon by sputtering. The resultant block was cut by a dicingmachine to obtain a piezoelectric resonator 10 measuring approximately1.5 mm by 1.5 mm by 3.8 mm.

The piezoelectric resonator 10 had nineteen electrodes 14 in the basemember 12, the electrodes 14 being disposed at an almost equal intervalof about 0.19 mm. Insulating films 16 and 18 were formed so as to avoidapplying an electric field to three piezoelectric layers disposed atboth ends of the base member 12. An active section 24 included 14piezoelectric layers disposed at the approximate center of the basemember 12, and an inactive section 26 had three piezoelectric layers atboth ends. The piezoelectric resonator 10 had a capacitance of 830 pFand the frequency characteristics shown in FIG. 13. For comparison, thefrequency characteristics of a square-type vibration piezoelectricresonator is shown in FIG. 14. It is clearly seen from FIGS. 13 and 14that the piezoelectric resonator 10 according to the preferredembodiments of the present invention has much less spurious vibrationthan the square-shaped piezoelectric resonator.

Depending on the positions where active sections 24 and inactivesections 26 are located, the frequency difference ΔF between theresonant frequency and the antiresonant frequency changes. Inactivesections 26 can be provided, for example as shown in FIG. 15, at bothends and the approximate center of the base member 12. The finiteelement method was used to calculate changes in capacitance Cf andfrequency difference ΔF in the piezoelectric resonator for changingpositions of the active sections, where "a" indicates the distancebetween the center and an end of the piezoelectric resonator 10, "b"indicates the distance between the center and the center of gravity ofan active section 24, "c" indicates the length of the active sections24, W indicates the width of the base member 12, and T indicates thethickness of the base member 12. FIG. 16 shows the relationship betweenb/a, and the ratio of ΔF to the antiresonant frequency Fa, ΔF/Fa, andthe capacitance Cf with "a" being equal to about 1.89 mm, W and T equalto about 0.8 mm, "c" equal to about 0.86 mm, and b/a changing. From FIG.16, it is clearly seen that the capacitance Cf does not change accordingto the changing positions of the active sections 24. In contrast, it wasalso determined that ΔF decreases as the active sections approach thetwo opposite ends of the base member 12.

The frequency difference ΔF can be easily changed in the piezoelectricresonator 10 by changing the ratio of the active sections 24 to theinactive sections 26. with a changing active-section ratio, which is aratio of the length of the active section 24 to a total length of thebase member 12 in the piezoelectric resonator 10 shown in FIG. 12, theresonant frequency Fr, the antiresonant frequency Fa, the frequencydifference ΔF, and its rate of change were measured and are indicated inTable 4 and FIG. 17.

                  TABLE 4                                                         ______________________________________                                        Active-                                                                       section Active-                        ΔF                               length  section   Fr      Fa      ΔF                                                                           change                                 (mm)    ratio (%) (kHz)   (kHz)   (kHz)                                                                              rate (%)                               ______________________________________                                        1.80    100.0     1047.4  1163.4  115.9                                                                               0.0                                   1.70    94.4      1042.4  1163.4  120.9                                                                               4.3                                   1.60    88.9      1038.6  1163.4  124.8                                                                               7.6                                   1.53    85.0      1036.6  1163.4  126.8                                                                               9.4                                   1.50    83.3      1035.9  1163.4  127.5                                                                               9.9                                   1.40    77.8      1034.5  1163.4  128.9                                                                              11.2                                   1.35    75.0      1034.3  1163.4  129.1                                                                              11.4                                   1.30    72.2      1034.3  1163.4  129.0                                                                              11.3                                   1.20    66.7      1035.5  1163.4  127.9                                                                              10.3                                   1.17    65.0      1036.1  1163.4  127.2                                                                               9.7                                   1.10    61.1      1038.1  1163.4  125.3                                                                               8.1                                   1.00    55.6      1042.0  1163.4  121.4                                                                               4.7                                   0.90    50.0      1047.4  1163.4  115.9                                                                               0.0                                   0.80    44.4      1054.3  1163.4  109.1                                                                              -5.9                                   0.70    38.9      1062.7  1163.4  100.6                                                                              -13.2                                  0.60    33.3      1072.7  1163.4   90.7                                                                              -21.8                                  0.50    27.8      1084.2  1163.4   79.1                                                                              -31.7                                  0.40    22.2      1097.3  1163.4   66.1                                                                              -43.0                                  0.30    16.7      1111.9  1163.4   51.5                                                                              -55.6                                  0.20    11.1      1127.9  1163.4   35.5                                                                              -69.4                                  0.10     5.6      1145.2  1163.4   18.2                                                                              -84.3                                  ______________________________________                                    

FIG. 17 shows the relationship between the active-section ratio andchange in ΔF under the condition in which ΔF is set to 100% when theactive-section ratio is 100%, namely when an inactive section does notexist. It is clearly seen from FIG. 17 that ΔF is large at anactive-section ratio of 65% to 85% with the peak ΔF being obtained at anactive-section ratio of 75%. The peak value is larger by about 10% thanthe ΔF obtained when the active-section ratio is 100%, in other words,when an inactive section does not exist. The same ΔF is obtained atactive-section ratios of 50% and 100%. Therefore, to obtain apiezoelectric resonator having a large ΔF, the active-section ratioshould be set to be substantially equal to about 50% or more.

In the piezoelectric resonator 10, when 14 piezoelectric layersconstituted the active section 24 among 20 layers, the capacitance was830 pF. In contrast, when the active-section ratio was set to 100%,which means that only one piezoelectric layer was used, in other words,when electrodes were disposed at two opposite end surfaces of the basemember 12, with the same material and the same dimensions, thecapacitance was 3.0 pF. When all of the 24 piezoelectric layersconstituted the active section 24, the capacitance was 1185.6 pF. Bychanging the number of piezoelectric layers in the active section 24 ofthe base member 12 in the piezoelectric resonator 10, the capacitancecan easily be changed within a range of about 400-times differencebetween the minimum and maximum. Therefore, by changing the laminationstructure of the piezoelectric resonator 10, the capacitance can beselected from a wide range which provides a large degree of flexibilityand freedom in capacitance design.

In order to connect the electrodes 14 disposed inside the base member 12to the external electrodes 20 and 22, insulating films 16 and 18 havingwindows 50 may be provided such that every other electrode 14 is exposedas shown in FIG. 18. The external electrodes 20 and 22 are preferablyprovided on the insulating films 16 and 18, and the electrodes 14alternately connect to the two external electrodes 20 and 22. Twoexternal electrodes 20 and 22 may be disposed on one side surface of thebase member 12 as shown in FIG. 19. Insulating films 16 and 18 arepreferably disposed on one side surface of the base member 12 in atwo-row arrangement and two rows of connection sections are preferablyprovided. These two rows of insulating films 16 and 18 are disposedrespectively on every other electrode 14. On these two rows ofinsulating film 16 and 18, two rows of external electrodes 20 and 22 arepreferably disposed, respectively. The piezoelectric resonators havingthese modifications achieve the same advantages as the above-describedpiezoelectric resonator. Also in the piezoelectric resonator 10 in whichinternal electrodes 14 are alternately exposed at side surfaces of thebase member 12 as shown in FIG. 20, an active section 24 and inactivesections 26 can be provided.

The capacitance and ΔF of the piezoelectric resonator 10 in whichinternal electrodes 14 are alternately exposed as shown in FIG. 20 canbe changed by adjusting the opposing areas of adjacent electrodes 14.Using the finite element method, with the gap G between the end of anelectrode 14 and the side surface of the base member 12 in the thicknessdirection being changed, the antiresonant frequency Fa, capacitance Cf,and ΔF of a piezoelectric resonator having a base member 12 which isapproximately 3.74 mm long, 0.8 mm wide, 1.0 mm thick, and having anactive section 24 which is approximately 3.6 mm long, inactive sections26 disposed at both ends which are approximately 0.07 mm long and 20piezoelectric layers each being approximately 0.18 mm thick, as shown inFIG. 21, were calculated. The results are shown in Table 5 and FIG. 22.It is found from Table 5 and FIG. 22 that Cf and ΔF become smaller asthe gap G increases, in other words, as the opposite area of theelectrodes 14 becomes smaller.

                  TABLE 5                                                         ______________________________________                                                       Fa             Cf          ΔF                                           change         change      change                              Gap G  Fa      rate           rate   ΔF                                                                           rate                                (μm)                                                                              (kHz)   (%)      Cf (pF)                                                                             (%)    (kHz)                                                                              (%)                                 ______________________________________                                         1     546.37  -0.52    267.58                                                                              27.47  53.36                                                                              30.15                                50    546.75  -0.45    264.40                                                                              25.96  52.71                                                                              28.56                               100    547.38  -0.33    251.69                                                                              19.90  50.05                                                                              22.07                               150    548.20  -0.18    232.38                                                                              10.70  45.89                                                                              11.93                               200    549.20   0.00    209.91                                                                               0.00  41.00                                                                               0.00                               250    550.61   0.26    181.96                                                                              -13.32 35.06                                                                              -14.49                              300    552.11   0.53    156.44                                                                              -25.47 29.75                                                                              -27.44                              ______________________________________                                    

Electrodes 14 may be formed such that they extend to different endsurfaces on the same side of piezoelectric layers as shown in FIG. 23 ina piezoelectric resonator 10 which is a modified example of theabove-described piezoelectric resonator 10. By laminating these twotypes of piezoelectric layers, two rows of electrodes 14 are preferablyexposed on one side surface of the base member 12 as shown in FIG. 24.Therefore, by forming external electrodes 20 and 22 at portions wherethe electrodes 14 are exposed, the electrodes 14 are alternatelyconnected to the external electrodes 20 and 22.

In the piezoelectric resonator 10 in which each electrode 14 is formedto cover an entire cross section of the base member 12 as shown FIGS. 2and 12, since an electric field is applied to the entire cross sectionof the base member 12, the electromagnetic coupling coefficient of theresonator is large and thus ΔF is large. The capacitance of thepiezoelectric resonator 10 is therefore also large. When the laminatedblock is cut to produce a plurality of the piezoelectric resonators 10,since each electrode has been formed to cover almost the entire crosssection of the laminated block in advance, each piezoelectric resonatorhas an electrode which covers the entire cross section even if the cutposition shifts. Therefore, it is not necessary to precisely determinethe positions at which the laminated block is cut. By changing thedirection of cutting, resonators having different cross sections,different areas, and different capacitances are obtained from the samepiezoelectric, ceramic, laminated block. Resonators having variouscapacitances and various ΔF can be obtained according to which electrodeend section has insulating film. As described above, many types ofpiezoelectric resonators can be obtained from the same laminated block.

In contrast, to produce a piezoelectric resonator having a gap betweenan end of each electrode 14 and the side surface of the base member 12as shown in FIGS. 11 and 20, it is necessary to cut a laminated blockafter positioning such that the gap is correctly formed. In such apiezoelectric resonator, however, it is not necessary to provideinsulating film on a side surface of a base member, and the number ofmanufacturing steps is substantially reduced.

An inactive section 26 may be formed such that an electric field is notapplied by not providing electrodes 14 on an end of the base member 12as shown in FIG. 25. The end of the base member 12 may be polarized ormay not be polarized. As shown in FIG. 26, it is possible for only theend of the base member 12 to be not polarized. In this case, even if anelectric field is applied between the electrodes 14, a portion which isnot polarized is piezoelectrically inactive. In other words, only when apiezoelectric layer is polarized and an electric field is applied, doesthe layer become piezoelectrically active, otherwise the layer isinactive. In this configuration, the capacitor is disposed in theinactive section, and the capacitance is increased. A small electrode 52may be provided on an end surface of the base member 12 as shown in FIG.27 in order to adjust the frequency or to connect to an externalcircuit.

Using such a piezoelectric resonator 10, electronic components such asoscillators and discriminators are produced. FIG. 28 is a perspectiveview of an electronic component 60. The electronic component 60 includesan insulating substrate 62. At opposing end portions of the insulatingsubstrate 62, two indentations 64 are preferably formed, respectively.On one surface of the insulating substrate 62, two pattern electrodes 66and 68 are formed as shown in FIG. 29. One pattern electrode 66 isdisposed between opposing indentations and extends in a substantiallyL-shaped manner from a point near one end toward the center of theinsulating substrate 62. The other pattern electrode 68 is disposedbetween opposing indentations 64 and extends substantially straight froma point near the other end toward the center of the insulating substrate62. The pattern electrodes 66 and 68 are arranged such that they arerouted in a roundabout fashion from the ends of the insulating substrate62 to the opposite surface.

At one end of the pattern electrode 66 disposed at the center of theinsulating substrate 62, a protrusion 70 is formed with electricallyconductive adhesive. As shown in FIG. 30, the above-describedpiezoelectric resonator 10 is preferably mounted on the protrusion 70such that the approximate center of the base member 12 at a location ofa node point of the base member is disposed on the protrusion 70. Anexternal electrode 22 of the piezoelectric resonator 10 is, for example,connected to the protrusion 70. The other external electrode 20 isconnected to a pattern electrode 68 preferably with electricallyconductive wire 72. The electrically conductive wire 72 is preferablyconnected to the approximate center of the external electrode 20 of thepiezoelectric resonator 10. The protrusion 70 may be provided on thepiezoelectric resonator 10. In this case, the protrusion 70 provided forthe piezoelectric resonator 10 is mounted on the pattern electrode 66with electrically conductive adhesive.

A metal cap 74 is preferably placed on the insulating substrate 62 tocomplete the electronic component 60. To prevent the metal cap 74 frombeing short-circuited to the pattern electrodes 66 and 68, insulatingresin is preferably applied to the insulating substrate 62 and thepattern electrodes 66 and 68 in advance. The electronic component 60uses the pattern electrodes 66 and 68, which are arranged such that theyare routed to the rear surface from ends of the insulating substrate 62,as input and output terminals for connecting to external circuits.

Since the approximate center of the piezoelectric resonator 10 isconnected to the protrusion 70 in this electronic component 60, the endsof the piezoelectric resonator 10 are disposed separately from theinsulating substrate 62 so vibration is not prevented or damped. Excitedlongitudinal vibration is not weakened because the approximate center ofthe piezoelectric resonator, which serves as a node, is secured to theprotrusion 70 and is connected to the electrically conductive wire 72.

The electronic component 60 is preferably mounted on a circuit boardtogether with IC chips and other components to form an oscillator and adiscriminator. Since the electronic component 60 is sealed and protectedby the metal cap 74, it can be used as a chip-type, surface-mountablecomponent which can be mounted by reflow soldering or other suitablemethods.

When the electronic component 60 is used in an oscillator, spuriousvibrations are suppressed to a low level and unusual vibration caused bythe spurious vibrations are prevented due to the unique structure andarrangement of the piezoelectric resonator 10 used in the electroniccomponent 60. It is also easy to achieve impedance matching with anexternal circuit since the capacitance of the piezoelectric resonator 10can be set to any desired value. Especially when the electroniccomponent is used for an oscillator for voltage-controlled oscillation,a wide frequency range which cannot be obtained conventionally isachieved as a result of a large ΔF of the resonator.

When the electronic component 60 is used for a discriminator, a widepeak-separation range is achieved as a result of a large ΔF of theresonator. In addition, since the resonator provides a wide capacitancerange, it is easy to achieve impedance matching with an externalcircuit.

The piezoelectric resonator 10 may be preferably mounted on theinsulating substrate 62 so that two protrusions 70 made from anelectrically conductive material such as electrically conductiveadhesive are provided on both pattern electrodes 66 and 68, and theexternal electrodes 20 and 22 of the piezoelectric resonator 10 areconnected to the two protrusions 70, as shown in FIGS. 31 and 32. Thepiezoelectric resonator 10 may also be mounted on the insulatingsubstrate 62 in a way shown in FIGS. 33 and 34 in which two protrusions70 made from an insulating material such as insulating adhesive areformed on the insulating substrate 62 and the external electrodes 20 and22 are connected to the pattern electrodes 66 and 68 with electricallyconductive wire 72.

A ladder filter can be constructed to contain at least one, butpreferably, a plurality of the piezoelectric resonators 10. As shown inFIGS. 35 and 36, three pattern electrodes 76, 78, and 80 are disposed onan insulating substrate 62 in this electronic component 60. Protrusions82 and 86 are formed with electrically conductive adhesive on both-endpattern electrodes 76 and 80. On the center pattern electrode 78, twoprotrusions 84 and 88 are formed with electrically conductive adhesive.

One external electrode 22 for each of piezoelectric resonators 10a, 10b,10c, and 10d is mounted on each of the protrusions 82, 84, 86, and 88,respectively. The other external electrodes 20 for piezoelectricresonators 10a, 10b, and 10c are connected to each other withelectrically conductive wire 72. The other external electrode 20 of apiezoelectric resonator 10d is connected to the pattern electrode 80with electrically conductive wire 72. A metal cap 74 is placed on theinsulating substrate 62.

The electronic component 60 is used as a ladder filter having aladder-shaped circuit shown in FIG. 37. Two piezoelectric resonators 10aand 10c serve as series resonators and the other two piezoelectricresonators 10b and 10d serve as parallel resonators. In such a ladderfilter, the parallel piezoelectric resonators 10b and 10d are designedto have substantially larger capacitances than the series piezoelectricresonators 10a and 10c.

Attenuation in the ladder filter is determined by the capacitance ratiobetween the series resonators and the parallel resonators. In thiselectronic component 60, the capacitance can be adjusted by changing thenumber of laminated layers used in the piezoelectric resonators 10a to10d. Therefore, a ladder filter having a larger attenuation with fewerresonators is implemented by changing the capacitances of thepiezoelectric resonators, as compared with a case where the conventionalunstiffened piezoelectric resonators are used. Since the piezoelectricresonators 10a to 10d have a larger ΔF than the conventionalpiezoelectric resonator, a wider transmission frequency band is achievedas compared with the conventional piezoelectric resonator.

A two-terminal electronic component 60 such as a resonator and adiscriminator can be produced with a piezoelectric resonator 10 as shownin FIG. 38. Two terminals 90 made from an electrically conductivematerial are prepared to produce such a two-terminal component 60. Theseterminals 90 are formed such that they extend from hoops 92.Practically, a plurality of terminals 90 are formed on each hoop 92 andarranged in line. A terminal 90 is provided with a fold section 94 atthe intermediate portion and an H-shaped support member 96 at the end.The support member 96 is bent and is provided with a protruded mountingmember 98 at the center. The two terminals 90 are disposed such thattheir mounting members 98 oppose each other.

The piezoelectric resonator 10 is supported between the mounting members98. The mounting members 98 abut against the external electrodes 20 and22 preferably at the center of the piezoelectric resonator in thelongitudinal direction. Since the terminals 90 have fold sections 94,which serve as spring elements, the piezoelectric resonator 10 isspring-supported by the terminals 90. A case 100 having an opening atone end is placed on the piezoelectric resonator 10. The opening of thecase 100 is preferably closed with paper and then resin-sealed. Theterminals 90 are cut from the hoops 92 to complete the electroniccomponent 60. The electronic component 60 having a shape other than achip-shape can thus be made.

Since the base member 12 has a laminated structure, the capacitance ofthe piezoelectric resonator 10 according to the preferred embodiments ofthe present invention can be set to any desired value and it is easy toachieve impedance matching with an external circuit. Since the preferredembodiments of the present invention provide a stiffened piezoelectricresonator, the resonator has a larger ΔF and a wider frequency band thanthe conventional unstiffened piezoelectric resonator. In addition, thestiffened piezoelectric resonator has small spurious vibrations.Furthermore, by adjusting the sizes and positions of the active sectionand the inactive sections, ΔF can easily be changed. Since theelectronic component 60 according to the preferred embodiments of thepresent invention has a simple structure, it can be produced at a lowcost while achieving the above-described features and advantages of thepiezoelectric resonator 10.

Since the piezoelectric resonator 10 according to the preferredembodiments of the present invention includes more parameters which canbe designed than the conventional piezoelectric resonator, variousdesirable resonator characteristics are achieved. The relationshipsbetween these parameters, ΔF/Fa and capacitance Cf are indicated in FIG.39. It is understood from FIG. 39 that these parameters increase thedegree of flexibility and freedom in designing the characteristics ofthe piezoelectric resonator 10.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:
 1. A piezoelectric resonator comprising:apiezoelectric base member including a plurality of piezoelectric layersand a plurality of electrodes; means for driving said piezoelectric basemember; and a support substrate supporting said piezoelectric basemember; wherein at least two of said piezoelectric layers are stacked oneach other and at least one of said plurality of electrodes is disposedbetween said at least two of said piezoelectric layers and said at leasttwo of said piezoelectric layers are polarized in opposite directionssuch that a longitudinal basic vibration is generated in said basemember along a longitudinal axis of the piezoelectric base member andsaid piezoelectric base member is displaced along the longitudinal axiswhen said means for driving said piezoelectric base member applies anelectric field to said at least one of said plurality of electrodes andsuch that a single vibration node at which point substantially novibration occurs is defined at an approximate center of thepiezoelectric base member and said piezoelectric base member issupported on said support substrate only at a location of said singlevibration node located at the approximate center of the piezoelectricbase member.
 2. A piezoelectric resonator according to claim 1, whereinsaid plurality of piezoelectric layers and said plurality of electrodesare arranged in a laminated stack which defines an integral unit.
 3. Apiezoelectric resonator according to claim 1, wherein each of saidplurality of piezoelectric layers is arranged to vibrate in a thicknessvibrating mode and said plurality of piezoelectric layers and saidplurality of electrodes are arranged in a laminated stack such that saidbase member vibrates in a longitudinal vibration mode as an integralunit.
 4. A piezoelectric resonator according to claim 1, wherein saidplurality of piezoelectric layers and said plurality of electrodes arestacked and define an integral unit, each of said plurality ofelectrodes is disposed between adjacent ones of said piezoelectriclayers, each of said piezoelectric layers located between adjacent onesof the electrodes is polarized in a direction that is opposite to adirection of polarization of at least one adjacent piezoelectric layer.5. A piezoelectric resonator according to claim 1, wherein said basemember is polarized in opposite directions at both sides of at least oneof said plurality of electrodes.
 6. A piezoelectric resonator accordingto claim 1, wherein said base member includes an active sectionconstituting a first portion of said base member and at least oneinactive section constituting a second portion of said piezoelectricbase member.
 7. A piezoelectric resonator according to claim 6, whereinsaid active section is polarized in a longitudinal direction of saidbase member and arranged to generate a longitudinal vibration in saidbase member when an electric field is applied in the longitudinaldirection of said base member, said at least one inactive section is notpolarized or not energized by an electric field.
 8. A piezoelectricresonator according to claim 6, wherein said at least one inactivesection is disposed at one of two opposite ends of said active sectionand extends to an end at said base member.
 9. A piezoelectric resonatoraccording to claim 6, wherein said active section occupies at leastapproximately 50% of the length of said base member which extends in thelongitudinal direction of said base member.
 10. A piezoelectricresonator according to claim 1, wherein said plurality of electrodes arearranged substantially perpendicular to a longitudinal direction of saidbase member.
 11. A piezoelectric resonator according to claim 1, whereinsaid at least one pair of electrodes comprise internal electrodes, thepiezoelectric resonator further comprising a pair of external electrodeseach disposed on one of two opposite side surfaces of the base memberand extending along a length of the base member.
 12. A piezoelectricresonator according to claim 1, wherein said plurality of electrodeseach includes an exposed portion which extends to an external surface ofthe base member, wherein the plurality of electrodes are alternatelycovered by insulating film disposed on opposite side surfaces of thebase member such that each insulating film covers an exposed portion ofevery other one of the plurality of electrodes.
 13. A piezoelectricresonator comprising:a piezoelectric base member including a pluralityof piezoelectric layers and a plurality of electrodes; means for drivingsaid piezoelectric base member; and a support substrate supporting saidpiezoelectric base member; wherein said plurality of piezoelectriclayers and said plurality of electrodes are arranged in a laminatedstack which defines an integral unit and which is arranged such thatwhen said means for vibrating said piezoelectric base member applies anelectric field to the piezoelectric base member, the piezoelectric basemember vibrates in a longitudinal vibration mode along a longitudinalaxis of the piezoelectric base member and said piezoelectric base memberis displaced along the longitudinal axis such that a single vibrationnode at which point substantially no vibration occurs is defined at anapproximate center of the piezoelectric base member and saidpiezoelectric base member is supported on said support substrate only ata location of said single vibration node located at the approximatecenter of the piezoelectric base member.
 14. A piezoelectric resonatorcomprising:a piezoelectric base member including a plurality ofpiezoelectric layers and a plurality of electrodes; means for drivingsaid piezoelectric base member; and a support substrate supporting saidpiezoelectric base member; wherein each of said plurality ofpiezoelectric layers is arranged to vibrate in a thickness mode and saidplurality of piezoelectric layers and said plurality of electrodes arearranged in an integral stack such that when said means for vibratingsaid piezoelectric base member applies an electric field to thepiezoelectric base member, said base member vibrates in a longitudinalvibration mode along a longitudinal axis of the piezoelectric basemember and said piezoelectric base member is displaced along thelongitudinal axis such that a single vibration node at which pointsubstantially no vibration occurs is defined at an approximate center ofthe piezoelectric base member and said piezoelectric base member issupported on said support substrate only at a location of said singlevibration node located at the approximate center of the piezoelectricbase member.
 15. An electronic component comprising:a substrate; amounting member mounted on said substrate; at least one piezoelectricresonator including a piezoelectric base member including a plurality ofpiezoelectric layers and a plurality of electrodes; means for drivingsaid at least one piezoelectric resonator; wherein at least two of saidpiezoelectric layers being stacked on each other and at least one ofsaid plurality of electrodes being disposed between said at least two ofsaid piezoelectric layers and said at least two of said piezoelectriclayers are polarized in opposite directions, and being arranged suchthat when said means for vibrating said piezoelectric base memberapplies an electric field to the piezoelectric base member, thepiezoelectric base member vibrates in a longitudinal vibration modealong a longitudinal axis of the piezoelectric base member and saidpiezoelectric base member is displaced along the longitudinal axis suchthat a single vibration node at which point substantially no vibrationoccurs is defined at an approximate center of the piezoelectric basemember and such that a vibration node at which point substantially novibration occurs is defined at an approximate center of thepiezoelectric base member, said at least one piezoelectric resonatorbeing mounted on said substrate via said mounting member such that thepiezoelectric base member is supported only at said single node point atthe approximate center of the piezoelectric base member; a cap disposedon said substrate for covering said base member.
 16. An electroniccomponent comprising:a substrate having a pattern electrode disposedthereon; a mounting member mounted on said pattern electrode on saidsubstrate; a plurality of piezoelectric resonators including apiezoelectric base member containing a plurality of piezoelectric layersand a plurality of internal electrodes; means for vibrating saidplurality of piezoelectric resonators; wherein at least two of saidpiezoelectric layers being stacked on each other and at least one ofsaid plurality of electrodes is disposed between said at least two ofsaid piezoelectric layers and said at least two of said piezoelectriclayers are polarized in opposite directions and are arranged such thatwhen said means for vibrating said piezoelectric base member applies anelectric field to the piezoelectric base member, the piezoelectric basemember vibrates in a longitudinal vibration mode along a longitudinalaxis of the piezoelectric base member and said piezoelectric base memberis displaced along the longitudinal axis such that a single vibrationnode at which point substantially no vibration occurs is defined at anapproximate center of the piezoelectric base member, said piezoelectricbase member including at least one pair of external electrodes beingarranged such that each of said plurality of internal electrodes iselectrically connected to one of said at least one pair of externalelectrodes, said at least one piezoelectric resonator being mounted onsaid pattern electrode on said substrate via said mounting member suchthat said pattern electrode is electrically connected to said at leastone pair of external electrodes such that the piezoelectric base memberis supported only at said single node point at the approximate center ofthe piezoelectric base member; and a cap disposed on said substrate forcovering said base member.